Ram type blowout preventer



Dec. 13, 1960 Filed April 1, 1958 H. ALLEN RAM TYPE BLOWOUT PREVENTER 4Sheets-Sheet 1 Herberf A/ln INVENTOR.

ATTORNEYS Dec. 13, 1960 H. ALLEN RAM TYPE BLOWOUT PREVENTER Filed April1, 1958 4 Sheets-Sheet 2 Herbs/f A //@/7 INVENTOR.

Dec. 13, 1960 H. ALLEN RAM TYPE BLOWOUT PREVENTER 4 Sheets-Sheet 5 FiledApril 1, 1958 Herber f A //e/? Dec. 13, 1960 H. ALLEN RAM TYPE BLOWOUTPREVENTER 4 Sheets-Sheet 4 Filed April 1, 1958 QM. f

I Herbert /l///7 kfJBY I i M'Mv 'INVENTOR.

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United States Patent F RAM TYPE BLOWOUT PREVENTER Herbert Allen,Houston, Tex., assignor to Cameron Iron Works, Inc., Houston, Tex.

Filed Apr. 1, 1958, Ser. No. 725,577

11 Claims. (Cl. 251-1) This invention relates to ram type blowoutpreventers and, more particularly, to improvements in that type ofblowout preventer in which the rams are moved between opened and closedpositions independently of one another.

There are several instances in which particular care must be exercisedto see that the rams of a blowout preventer are closed about a drillstring or other ppe substantially coaxially of the flowway therethrough.For example, it is sometimes desirable, in the drilling of petroleumwells, to install two blowout preventers one above the other and withtheir rams arrangedfor movement in angularly spaced apart verticalplanes, such as at right angles to one another. This would be impossibleif the pipe within the preventer were shoved off-center as the rams wereclosed thereabout. It may also be desirable to mount a preventer forrotation about the axis of the well bore, in which case an ofi-centerpipe would cause excessive vibration.

In the past, preventers designed for low pressure installations haveemployed interengaging operating mechanisms including gears or leadscrews which position the rams with respect to one another at all timesby applying all available force simultaneously to both rams. Referenceis made to Patent No. 1,963,683 for an example of such a preventer.Although preventers having manual operators of this type might insurethat the pipe within the flowway is not shoved off-center, they are notpractical for present day usage because higher pressure applications andlarger sizes of preventers have produced correspondingly largeroperating force requirements for the rams which almost preclude theiruse.

Accordingly, manufacturers of such equipment have resorted to poweroperators, the most practical embodiment of which has one or more fluidpressure pistons connected to each ram for moving them between openedand closed positions independently of one another. An example of apreventer having such power operators is shown in Patent No. 2,387,106.In this, as well as other preventers of this general type, one ram willalmost invariably move into closing position prior to the other. This isdue to the fact that the frictional resistance to travel of the one ramis greater, even though by a small amount, than the frictionalresistance to travel of the other ram.

It is conventional to limit the closing movement of the rams of blowoutpreventers of this type to prevent them from extending so far into theflowway as to lose their support. For example, in the particularpreventer abovementioned, a yoke secured to each piston rod limits ramtravel by bearing against the bonnet of the preventer body. However, inorder to allow for wear upon the front packing of the rams, to providefor extruding the packing and developing high sealing pressure, and toprovide for manufacturing tolerances, it is also conventional to locatethe limits or stops in such'a manner as to permit overtravel of therams.

Even though such overtravel may be small, it is sufli- "ice otherbecause the pipe, which is long and free hanging, provides littleresistance to the force of the rams. More particularly, the pipe seldomprovides resistance sufiicient to offset the greater frictionalresistance to travel of one of the rams than the frictional resistanceto travel of the other ram. The problem is additionally acute in thecase of preventers having universal rams, of the type shown in JonesPatent No. 2,746,710, because such rams, in closing and sealing aboutpipes of different diameter as well as with one another when no pipe isdisposed within the flowway, obviously need considerably less travel inclosing about large pipes than they do in closing against one another.

An object of this invention is to provide a blowout preventer in whichthe rams are moved independently of one another between positionsopening and closing the flowway without shoving a pipe disposed therein0&- center.

Another object is to provide a blowout preventer of the type abovedescribed in which the closing movement of the rams is synchronized by amechanism which takes full advantage of the relationship between theforce tending to prevent one ram from moving with the other and the ramoperating forces; and, more particularly, which takes advantage of theabove-noted fact that the firstmentioned force is of small magnitude incomparison to the latter.

A further object is to provide a blowout preventer of the characterdescribed in the foregoing object in which the rams are synchronizedwith a minimum of restraint upon their normal operation.

A still further object is to provide a mechanism of the character abovedescribed which is easily and readily manually manipulatable in theevent of mechanical failure which might otherwise prevent completeclosure of the rams.

Still another object is to provide a mechanism of the characterdescribed in the foregoing objects which will not interfere with theeffect of well pressure behind the rams for urging them into sealingengagement about the pipe and with one another.

These and other objects are accomplished, in accordance with the presentinvention, by a blowout preventer which comprises a body having aflowway therethrough and openings therein intersecting the flowway, aram in each of said openings, operating means for moving the ramsindependently of one another between positions opening and closing theflowway, and means for 'substantially synchronizing closing movement ofthe rams to cause them to close about a pipe axially within the flowwaysubstantially simultaneously with one another. This synchronizing meanscomprises parts movable in response to movement of each ram into closingposition, and means on the body engageable by said parts during closingmovement of the rams and yieldable, in response to such movement thereofin substantial unison with one another, to permit said rams to closeabout a pipe in the manner described.

In accordance with one embodiment of the invention, the synchronizingmeans is operative to cause the rams to move in substantial unison withone another during only a predetermined final stage of closing movementthereof such that the normal operation of the rams is restrained duringonly this final stage. More particularly, the yieldable means is adaptedto stop one of the rams when it begins its final stage of closingmovement until the other ram also reaches its final stage, and thenprevent each ram from moving at a substantially faster rate than theother during such final stage so that they continue to move into closedposition in substantial unison with one another.

The stop means of the above-described embodiment preferably comprises ahead member having a stem slidably received within an opening in thebody and opposite ends engageable by the movable parts to place'aneccentric loading on the stem when it engages said member which, whensubstantially unbalanced, prevents the stem from sliding within theopening. The ends of the head member and movable parts are so arranged,however, that the eccentric loadings substantially balance one anotherto permit sliding of the stem within the body opening when each of saidparts is moved into engagement with the head member and the ramscontinue to move into closed position in substantial unison 'with oneanother.

More particularly, the head member is disposed on the exterior of thebody so thatit may be jarred to free the stem should it become stuck andfail to slide within the body opening, as intended. Spring means areprovided for urging the'head member to a position for engagement by themovable parts when the rains are returned to their open position, suchthat the synchronizing means is automatically prepared for the next ramclosing.

In accordance with another embodiment of the invention, each of saidmovable parts comprises a cylinder, and the yieldable means includespistons secured to the body and slidable within each of the cylinders,and means for hydraulically connecting the cylinders to one anotheronopposite sides of'the pistons for moving said cylinders in unison withone another.

More particularly, in a preferred form of the abovedescribed embodiment,the yieldable means comprises a rod secured to the body for extensionconcentrically through the cylinders and having spaced apart pistonsthereon slidable within said cylinders. Spaced apart heads on eachcylinder are slidable over the rod at opposite sides of each pistonthereon to form concentric pressure chambers on opposite sides of therod pistons, and conduits connect the outermost chamber of each cylinderwith the innermost chamber of the other. Still further, the rodcomprises a pair of concentrically arranged tubular members which areclosed at opposite ends and connected to the chambers to form theconduits within the rod.

In the drawings, wherein like reference characters are used throughoutto designate like parts:

Fig. 1 is a side elevational view of a blowout preventer havingsynchronizing means constructed in accordance with the first-mentionedembodiment of the present invention, with the rams of such preventer infiowway opening position and one side of the body broken away in part toshow an internal portion of the operator engaged with one of the rams;

Fig. 2 is a cross-sectional view of the blowout preventer of Fig. 1,taken substantially along broken line 22 of Fig. 1;

Figs. 3 to 5 are elevational views of the rams and synchronizing meansremoved from the preventer body of Figs. 1 and 2, and shown sequentiallyin the positions they occupy as the rams are closed about a pipe;

Fig. 6 is an elevational view of a blowout preventer identical to thatof Figs. 1 to 5 except for another form of synchronizing means, and withpart of the external portion of the operator for the rams shown insection;

Fig. 7 is a partial and elevational view of the blowout preventer ofFig. 6 with the synchronizing means thereof in section, as seen alongbroken lines 77 of Fig. 6;

Fig. 8 is a side view, partly in elevation and partly in section, of ablowout preventer having synchronizing means constructed in accordancewith the second-mentioned embodiment of tthe present invention, and withthe rams of such preventer in fiowway opening position;

Fig. 9 is an enlarged side view of the synchronizing means of theblowout preventer of Fig. 8, with one side thereof broken away and in aposition occupied during the early'stages ofclosin'g movement of'therains; and

Fig. 10 is a sectional view of the top of the synchronizing means, in aposition occupied during a later stage of closing movement of the rams.

Referring now in detail to the above-described drawings, the blowoutpreventer 10 (Figs. 1, 2, 6 and 7) of the first embodiment of theinvention comprises a body 11 having a vertical fiowway 12 therethroughand transverse openings 13 (see Figs. 1 and 2) therein intersecting thefiowway at opposite sides thereof. Rams 14 within the openings 13 areconnected by an operator, designated in its entirety by referencecharacter 15, for sliding movement independently of one another betweenpositions opening (see Fig. '1) and closing the fiowway 12, in whichlatter position they engage and seal about a pipe 16 (see Figs. 3 to 5)disposed within the fiowway as well as with one another.

The top and bottom of the body 11 of the blowout preventer are providedwith flanges 17 for connection to other wellhead members with thefiowway 12 therethrough aligned with openings through such othermembers. Bonnets 18 are releasably securable to opposite ends of thebody by means of bolts 19 for covering the outer ends of openings 13.

Each of the rams 14 conventionally comprises a rigid body having a stripof resilient sealing material which includes a portion 20a extendingacross the inner end thereof, portions 2% extending from portion 20aalong opposite sides of the body, and portion 200 extending upwardlyacross the top thereof. The inner end of the body of each ram, includingthe portion 20a of the seal strip, is provided with a groove 21 forfitting about the pipe 16. More particularly, the portion 20a of theseal strip protrudes from the inner end of the ram body so that, as therams are moved into engagement about the pipe and with one another, theportions 2% and 20c will be forced into tight sealing engagement withthe openings 13 for the rams. As is conventionally the case in ram typeblowout preventers having operating means of this type, the closingforce upon the rams is supplemented by well pressure acting upon therear end of the rams, as will be understood from Figs. 1 and 2.

The aforementioned operator 15 for the rams comprises shafts 22journaled for rotation in each side of the preventer body 11 beneath theopenings 13 therein and a crank arm 23 (see Figs. 1 and 2) fixed to aninner end of each shaft for rotation therewith. A roller 24 on the free'end of each inner crank arm is disposed within a slot 25 in each ram,as shown in Fig. 1, so that the crank arms are swingable to move therams between fiowway opening and closing positions in response torotation of the shafts.

The shafts 22 are rotated for the purpose above mentioned by means ofcrank arms 26 which are keyed to outwardly extending portions of theshafts and pivotally connected by pins 26a at their free ends to acylinder 27 and a piston rod 28 having a piston 29 slidably receivedwithin the cylinder 27, as best shown in Fig. 6. The cylinder isprovided with ports 30 and 31 communicating therewith on opposite sidesof the piston 29 so that hydraulic fluid may be admitted and exhaustedtherefrom for extending and retracting the distance between the pins 26afor rotating the shafts 22 about their journals. Thus, upon theadmission of hydraulic fluid to port 31 and exhaustion thereof from port30, the piston rod 28 is retracted to move the rams to fiowway closingposition. On the other hand, the admission of hydraulic fluid to port 30and exhaustion thereof from port 31 will extend the piston rod andthereby move the rams to the fiowway opening position of Fig. 1.

A blowout preventer having rams and an operator of the general typeabove described is shown and describedin greater detail in my copendingapplication, Serial No. 673,299, filed July 22, 1957, and entitled ValveApparatus. Since the novel construction of such rams. and operator donot form part of the.present invention, which is also applicable toblowout preventers having rams and operators of more conventionalconstruction, these details will not be repeated herein.

However, as previously mentioned, with an operator of this or othertypes in which the rams are connected for movement independently of oneanother, it would be quite possible, without the synchronizing means ofthe present invention, for one ram to lead the other ram into itsflowway closing position and shove a pipe within the flowway to one sideof the axis thereof.

In accordance with the form of such synchronizing means which is shownin Figs. 1 to 5, a bracket 32 is secured to the side of the preventerbody approximately intermediate the shafts 22 and crank arms 26, and isprovided with a vertically extending rectangular opening 33 therein toslidably receive a similarly shaped stem 34 on a head member 35. Theopposite ends 36 of the head member overhang the stem and provide uppersurfaces for engagement by pins 37 on the inner ends of pins 26a as thecrank arms 26 are swung into positions for moving the rams into apredetermined final stage of closing movement, as shown by the leftmostram and pin 37 in Fig. 3 and both rams and pins in Fig. 4. It will beunderstood from each of these figures,'particularly in comparison withFig. 5, that the seal strip portions 20a of the rams have not at thisstage of closing movement tightly sealed about the pipe 16 and withrespect to one another.

The pins 37 and the surfaces on the overhanging ends 36 of the headmember are so arranged that the pins exert forces thereon havingvertical components spaced to one side of the vertical axis of the stem34. Thus, when one ram reaches its predetermined final stage of closingmovement prior to the other, as shown by the leftmost ram in Fig. 3, thepin 37 on the crank arm therefor loads the head member eccentrically totilt the stem thereof in a counterclockwise direction within the bracketopening. Consequently, the sides of the stem bear against the sides ofthe opening with a force acting normal thereto, and the frictionalcomponent of this force acts parallel to the stern in opposition to thedownward force on the stem so as to prevent downward movement of thestern.

However, with the crank arm 26 and pins 37 arranged symmetrically of thehead member, as shown, the eccentric loading upon the head member willbe balanced by a force due to the engagement of the pin 37 on the crankarm 26 for the rightmost ram with the rightmost overhanging end of thehead member as the rightmost ram moves into its predetermined finalstage of closing movement. That is, both pins 37 engage the ends 36 onthe head member with forces having vertical components which set upequal and opposite moments, so that the stem 34 of the head member isfree to slide downwardly within the opening 33.

However, should one of the rams again move into a leading positionduring its final stage of closing movement, such that the pin 37 of theouter crank arm therefor moves downwardly at a faster. rate than theother pin, the head member will again be eccentrically loaded, such thatthe frictional forces above described are again set up. Thus, sliding ofthe stem within the opening will again be stopped until the trailing ramreaches substantially the same position in its final closing movement asthe leading ram. At this time, the pin 37 on the crank arm connected tothe trailing ram will have been swung to a position which substantiallybalances the eccentric loading due to the pin on the other outer crankarm, so that the frictional forces previously described are eithereliminated or reduced to such a point that the stem will slidedownwardly within the opening in the bracket 32. In this manner, therams are caused to move in substantial unison with one another, duringtheir predetermined final stage of closing movement, until they reachtheir final closed position, as shown in Fig. 5. During this finalstage, the synchronizing means in no way interferes with the effect ofwell pressure acting upon the rear end of the rams.

With the head member 35 disposed exteriorly of the preventer body, itmay be jarred by a suitable tool should its stern become stuck withinthe bracket opening. The top portion of the head member intermediate theoverhanging ends 36 thereof is conveniently exposed for this purpose.

A boss 38 on the outer side of bracket 32 is provided with an openingtherethrough to slidably receive a rod 39 secured at its upper endwithin an opening in a boss 40 on the outer side of head member 35, asbest shown in Fig. 2. The lowermost end of the rod 39 is enlarged at 41to abut with the bottom of boss 38, and a coil spring 42 is arrangedabout the rod 39 and between the bosses 38 and 40 for urging the headmember upward. Thus, when the outer crank arms 26 are swung in oppositedirections so as to move the rams to open position, the head member willbe returned automatically by the spring 42 to a position in which it isdisposed for engagement by the pins 37 as the rams are moved into theirpredetermined final stages of closed movement.

In the form of the synchronizing means shown in Figs. 6 and 7, a bracket43 is secured to the side of the blowout preventer body substantiallyintermediate the shafts 22 and is provided with an opening 44therethrough for receiving a stem 45 upon a head member 46. Asdistinguished from the bracket opening and head member stem from theform of Figs. 1 to 5, each of the opening 44 and stem 45 of theembodiment of Figs. 6 and 7 is cylindrical. Furthermore, the overhangingends 47 of the head member 46 which provide the surfaces for engagementby the pins 48 (see Fig. 7) on the crank arms 26 are curvedsubstantially throughout their entire length.

Obviously, the top of head member 46 intermediate overhanging ends 47may be jarred to loosen the stem 45 in the same manner as the embodimentof Figs. 1 to 5.

A plate 49 welded or otherwise secured to the open lower end of thebracket 43 beneath the opening 44 therein is provided with an openingtherethrough substantially coaxially of opening 44 to slidably receive arod 50 threadedly secured at its upper end 51 to an intermediate portionof the head member 46. 'An enlarged portion 52 on the lower end of rod50 is engageable with the bottom side of plate 49, and a coil spring 53is disposed about the rod 50 intermediate the top side of the plate andthe aforementioned intermediate portion of the head member 46 so as tourge the head member to a position for engagement by the pins 48 uponmovement of the rams into their predetermined final stages of closingmovement.

The hollow stern and bracket protect the coil spring against damage. Inother respects, this form functions in substantially the same manner asthat previously described in connection with Figs. 1 to 5.

The blowout preventer 60 of the second embodiment of the invention isshown in Fig. 8 to comprise a body 61 having a vertical flowway 62therethrough and transverse openings 63 therein intersecting the flowwayat opposite sides thereof. As in the case of the previously describedembodiment, rams 64 within the openings 63 are connected by an operator,designated in its entirety by reference character 65, for slidingmovement independently of one another between positions opening (seeFig. 8) and closing the flowway, in which latter position they engageand seal about a pipe 66 disposed within the flowway as well as with oneanother.

The top and bottom of the preventer body 61 are provided with flanges 67for connection to other wellhead members, such as shown at 68, with theflowway 62 therethrough aligned with openings through such othermembers, such as shown at 69. Bonnets 70 are releasably securable toopposite ends of the body by suitable 7 means (not shown) for coveringthe outer'ends of the openings'63.

Each of the ra'ms '64 conventionally co'mprises'a rigid body having astrip of resilient sealing material which includes a portion 71extending across'the inner end thereof, a portion 72 extending acrossthe top thereof, and other portions (not shown) extending along oppositesides of the rigid body to connect the portions 71 and 72. As previouslydescribed in connection with the first embodiment of the invention, theinner end of the body of each ram, including the sealing strip portion71, is provided with a vertical groove for fitting'about the pipe 66.More particularly, this laterally extending portion 71 of the seal stripprotrudes from the inner'end of the ram body so as to force the side andtop portions of the sealing strip into tight sealing engagement with theopenings 63 as the rams are moved into engagement about the pipe andwith one another. The closing force exerted on the rams through theoperator '65 is supplemented by well pressure having access to the rearends of the rams through passages 73, as shown in Fig. 8.

The operator 65 for'the rams 64 of this embodiment of the inventioncomprises stems 74 having lugs 75 on their inner ends releasablyconnected to the rear ends of the rams and sealably received through thebonnets 70 for threaded connection at their outer ends with cross arms76. Each such cross arm extends laterally of one end of the body and'isprovided with a rod 77 (see the left side of Fig. 8) at each end forconnection with pistons 78 received with cylinders '79 mounted onopposite sides of the preventer body. Thus, as can be seen from Fig. 8,hydraulic fluid may be introduced to and exhausted from opposite sidesof the pistons 78 for moving the rams independently of one anotherbetween opened and closed positions.

Each of the bonnets 70 also includes a yoke 80 and a limit screw 81mounted in the yoke for movement parallel to the ram movement. The innerends 82 of the limit screws are thus engageable with the cross arms 76so as to limit opening movement of-the rams, as best shown on the rightside of Fig. 8, and also provide a means for manually moving each raminwardly into flowway closing position in the event of a power failure.

A blowout preventer having rams and an operator of the general typeabove described is shown and described in greater detail in theaforementioned Patent No. 2,387,l06. Since the construction of such ramsand operator do not form part of the present invention, such detailswill not be repeated herein. However, as previously mentioned withregard to the operator of the first embodiment of the invention,'itwouldbe quite possible, without the synchronizing means to be describedbelow, for one of the rams 64 to lead the other one into its flowwayclosingposition and thus-shove the pipe 66 to oneside-of the axis of theflowway 62.

"As shown in Fig. as well as the right hand sides of Figs. 8 and 9,thes-ynchronizing means of the second embodiment of the inventioncomprises a cylinder 83 connected by a bracket 84 to each cross arm 76at one side the-rodSS is fixed against movement with respect to thepreventer body.

Pistons 87 on the rod on each side of the bracket 86 are provided withseal rings 88 about their outer diameters for sealably sliding withinthe inner diameter of the cylinder during reciprocation of the cylinderswith respect to the rod. With the pistons 87 removably fitted about therod 85, as shown, seal rings 89 on their inner diameters are sealablyengageable with the outer diameter 'of the rod.

Each of the cylinders =83 is provided with a head 90 sealably slidableover the rod inwardly of the piston 87 thereon and a head 91 slidablethereover outwardly of such rod .piston. These cylinder heads may alsobe removably connected to the cylinders, and are thus provided with sealrings 92 about their outer diameters sealably engageable with the insidediameter of the cylinders and seal rings 93 on their inner diameterproviding a sliding seal with respect to the outside diameter of the rod85 during reciprocation thereover.

Thus, the pistons 87 and the heads and 91 form inner and outerconcentric pressure chambers 94 and 95, respectively, within eachcylinder. As shown in Fig. 10, the rod 85 comprises a pair ofconcentrically arranged tubular members 96 and 97 which are closed attheir opposite ends by plugs 85a to form inner and outer conduits 98 and99, respectively, extending longitudinally of the rod. Ports 100 and 101bridge the conduit 99 to connect the innermost chamber 94 within onecylinder (rightmost in Figs. 8 to 10) with the outermost chamber of theother cylinder (leftmost in Figs. 8 to 10). Ports 102 and 103 throughouter tubular member 97 connect the outermost chamber 95 of thefirst-mentioned cylinder with the innermost chamber 94 of the othercylinder.

The rod conduits and the chambers are filled with a suitable hydraulicfluid, such that as each ram is moved inwardly from the position of Fig.8, for example, to that of Fig. 10, the innermost chambers 94 of eachcylinder are increased in volume an amount corresponding to the decreasein volume of the outermost chambers 95 of the other cylinder. Thus, therod 85, its pistons and the hydraulic fluid within the pressure chambersand rod conduits provide a yieldable connection which is engageable withthe heads of the cylinders to move one in substantial unison with theother.

From the foregoing it will be seen that this invention is one welladapted to attain all of the ends and objects hereinabove set forth,together with other advantages which are obvious and which are inherentto the apparatus.

It will be understood that certain features and subcombinations are ofutility and may be employed without reference to other features andsubcombinations. This is contemplated by and is within the scope of theclaims.

As many possible embodiments may be made of the invention withoutdeparting from the scope thereof, it is to be understood that all matterherein set forth or shown in the accompanying drawings is to beinterpreted as illustrative and not in a limiting sense.

The invention having been described, what is claimed is:

1. A blowout preventer, comprising a body having a flowway therethroughand openings therein intersecting the flowway, a ram in each of saidopenings, operating means for moving the rams independently of oneanother between positions opening and closing the flowway, and means forstopping one of said rams when it reaches a predetermined final stage ofclosing movement prior to the other ram reaching a predetermined finalstage of closing movement until the other ram has reached saidpredetermined final stage thereof and then preventing each ram frommoving at a substantially faster rate than the other during such finalstage.

2. A blowout preventer, comprising a body having a flowway therethroughand openings therein intersecting the flowway, a ram in each of saidopenings, operating means for moving the rams independently of oneanother between positions opening and closing the flowway, a partmovable in response to movement of each ram into closing position, andstop means on the body engageable by said parts upon movement of eachram into a predetermined final stage of closing movement to interruptclosing movement thereof when one ram moves into its final stage ofclosingmovemem vprior to the other and yieldable so that .the rams will.close when both parts are engaged therewith and said rams continue tomove toward closed position in substantial unison with one another.

3. A blowout preventer, comprising a body having a flowway therethroughand openings therein intersecting the flowway, a ram in each of saidopenings, operating means for moving the rams independently of oneanother between positions opening and closing the flowway, parts movablein response to movement of each ram into closing position, and means onthe body engageable by said parts during closing movement of the rams toprevent each ram from moving at a substantially faster rate than theother ram during closing movement thereof and yieldable, in response tosuch movement thereof in substantial unison with one another, so thatthe rams will close about a pipe axially within the flowwaysubstantially simultaneously with one another.

4. A blowout preventer of the character defined in claim 3, wherein eachpart comprises a cylinder movable with a ram, and said yieldable meansincludes pistons secured to the body and slidable within each of thecylinders, and means for hydraulically connecting the cylinders to oneanother on opposite sides of the pistons for moving said cylinders inunison with one another.

5. A blowout preventer of the character defined in claim 3, wherein saidyieldable means comprises a head member having a stem slidably receivedin an opening in the body and opposite ends engageable by the movableparts to place an eccentric load on the head member when the partmovable in response to movement of one ram engages therewith prior tothe part movable in response to movement of the other ram, which load,when substantially unbalanced, prevents sliding of the stem within theopening, said ends of the head member and movable parts being arrangedto substantially balance said eccentric loads and permit said stem toslide within said opening when both of said parts engaging said ends ofsaid head member move into closed position in substantial unison withone another.

6. A blowout preventer, comprising a body having a flowway therethroughthe openings therein intersecting the flowway, a ram in each of saidopenings, operating means for moving the rams independently of oneanother between positions opening and closing the flowway, a cylindermovable with each ram, a rod secured to the body for extensionconcentrically through the cylinders, spaced apart pistons on the rodslidable within 10 the cylinders, spaced apart heads on each cylinderslidable over the rod at opposite sides of each piston thereon to formconcentric pressure chambers on opposite sides of the rod pistons, andconduits hydraulically connecting the outermost chamber of each cylinderwith the innermost chamber of the other.

7. A blowout preventer of the character defined in claim 6, wherein saidconduits are formed within the rod.

8. A blowout preventer of the character defined in claim 7, wherein saidrod comprises a pair of concentrically arranged tubular members closedat opposite ends and connected to the chambers to form said conduits.

9. A blowout preventer, comprising a body having a flowway therethroughand openings therein intersecting the flowway, a ram in each of saidopenings, operating means for moving the rams independently of oneanother between positions opening and closing the flowway, a head memberhaving a stem slidably received within an opening in the body, and partsmovable in response to movement of each of the rams into a predeterminedfinal stage of closing movement to engage the head member and place aneccentric loading thereon when the part movable in response to movementof one ram engages therewith prior to the part movable in response tomovement of the other ram, which loading, when substantially unbalanced,prevents sliding of the stern within the opening, said head member andmovable parts being arranged to substantially balance said eccentricloads and permit said stem to slide within said opening when both ofsaid parts engage said head member and said rams continue to move intoclosed position in substantial unison with one another.

10. A blowout preventer of the character defined in claim 9, whereinsaid head member is disposed on the exterior of the body.

11. A blowout preventer of the character defined in claim 9, includingspring means urging said head member to a position for engagement bysaid parts.

References Cited in the file of this patent UNITED STATES PATENTS778,591 Layne Dec. 27, 1904 1,834,922 Abercrombie Dec. 8, 1922 2,308,099Obecny Ian. 12, 1943 2,387,106 Allen Oct. 16, 1945

